To escape the constraints of water-bound reproduction, the first terrestrial vertebrates evolved a group of membranes that surround and protect developing embryos. The "amnion" is one of these membranes. It surrounds and protects in amniotic fluid, the developing embryos of birds, reptiles and mammals. Terrestrial vertebrates began to diversify and exploit their new habitats when the need to reproduce in water no longer dictated the course of their lives. Occurring in conjunction with this reproductive freedom was the evolution of non-permeable skin (to avoid cutaneous water loss), different less toxic forms of nitrogen waste and more efficient forms of locomotion and feeding. This text gives a detailed treatment of these and other changes that occurred as vertebrates completed the transition from aquatic to terrestrial life. It integrates modern systematic methods with studies of functional and physiological processes, and illustrates how studies of paleobiology can be illuminated by studies of neontology.